Outdoor lighting systems use light fixtures that aim a lamp in a desired direction and are generally intended to keep moisture from the electrical wiring running through the light fixture. The lamp, such as a spot light or flood light, is aimed to illuminate a particular area. Light fixture mounting assemblies for such applications typically include adjustable connections that allow the user to aim the light when the light fixture is installed, and various seals to keep moisture out of the light fixture.
A knuckle joint between the lamp and a mounting member of the light fixture mounting assembly is often used to allow limited rotation of the lamp about the knuckle joint. Rotation in this plane is commonly referred to as “vertical” adjustment, although this designation is used only for convenient discussion, and does not necessarily represent rotation of the light in a vertical direction. One type of knuckle joint uses locking teeth or serrations on opposing faces of the knuckle joint halves. A screw through the axis of the knuckle joint holds the opposing locking teeth together once the light fixture has been aimed and the screw has been tightened. Unfortunately, the locking teeth provide only step-wise adjustment, and the screw must be loosened to provide sufficient clearance to rotate the teeth past each other when aiming the light fixture. The exact aiming of the light fixture is not apparent until the screw holding the knuckle joint halves together has been re-tightened. Precise aiming of a light fixture with a serrated knuckle joint can involve multiple iterations, and is often done using two persons.
Other types of light fixtures provide tapers on the mating halves of the knuckle joint. One type of light fixture provides a tapered post on one half of the knuckle joint that mates with a tapered hole in the other half of the knuckle joint. The locking screw is tightened to hold the tapered parts together. Loosening the locking screw allows the knuckle joint to smoothly rotate for aiming the light fixture. However, the tapered post has a relatively long taper at a typical taper angle of about 7–8 degrees. The long taper results in a thick knuckle joint, which is undesirable when using this type of knuckle joint with smaller light fixtures.
Another disadvantage of this design is that the wireway for the electrical wiring goes around the tapered post. Thus, the inner diameter of the wireway through the knuckle joint includes the tapered post. Rotating the knuckle can strain the wiring because the wiring wraps around the tapered post.
Another type of light fixture has a tapered structure between the faces of the knuckle halves outside (i.e. beyond the outer diameter) of the wireway. A ridge with a tapered face is formed on one knuckle half, and a groove with a tapered face is formed on the other knuckle half. The tapered face of the ridge mates with the tapered face of the groove. The tapered structure provides friction to hold the knuckle halves together when the locking screw is tight. This light fixture avoids straining the wiring around a thick central post when aiming the light fixture, but the tapered structure provides relatively little contact area. The fixture can come out of alignment if the locking screw is not sufficiently tight.
Unfortunately, if the locking screw of any of the above light fixtures loosens, the knuckle joint might rotate if even modest torque is applied, resulting in the light fixture coming out of alignment. The locking screw is particularly likely to loosen in applications where the light fixture is subject to vibration. For example, light fixtures near or on a ride at an amusement park, or adjacent to a cobblestone street, experience vibration that can loosen the locking screw. Similarly, some lamps are fairly heavy, and subjecting the light fixture to vibration might also provide sufficient torque on the loosened knuckle joint to cause the lamp to come out of alignment. Thus, it is desirable to provide a lighting fixture that more securely maintains its alignment, and is less susceptible to misalignment if the locking screw loosens.
In addition to allowing adjustment in the vertical direction, many light fixtures also allow rotational adjustment in the horizontal direction. “Horizontal” adjustment commonly refers to rotating the lamp about an axis that is orthogonal to the axis of the knuckle joint. Some light fixtures are horizontally adjusted by loosening a locking nut that holds the light mounting assembly to a mounting surface or outlet box, rotating the assembly, and tightening the locking nut. Access to the locking nut is typically behind the mounting surface or inside the outlet box, which makes horizontal adjustment difficult. This approach to horizontal adjustment is also trial-and-error, as the installer cannot view the aim of the light fixture until after the locking nut has been tightened and the light fixture is secured to the mounting surface or outlet box.
Another approach to horizontal adjustment uses a threaded stud that is secured to a mounting surface or outlet box. The stud is rotatably coupled to a base member of the light fixture. When the light fixture is horizontally rotated to the desired alignment, a set screw in the base member is tightened against the stud. However, the set screw has a limited contact area and tends to damage the finish, or even gouge, the surface of the stud. As with the locking screw of the knuckle joints, the set screw can loosen from a variety of causes, such as vibration. A slight loosening can allow the light fixture to come out of alignment. If the set screw is sufficiently loosened or removed, such as by a careless maintenance worker, the base member can fall away from the stud. Although the electrical wiring provides some attachment of the light fixture to its mounting surface, many light fixtures are quite heavy and the wiring might not hold the light fixture. Dropping the light fixture could damage the light fixture and cause injuries. Therefore, it is desirable to provide convenient, safe horizontal adjustment of light fixtures.
Horizontal adjustment techniques typically include some sort of device that limits rotating the light fixture to about one revolution with respect to the base. This is a safety requirement for many applications, and avoids undue strain on the wiring that might otherwise result from repeatedly wrapping or twisting the wiring. Some light fixtures include a stop member on the stud that interacts with a stop member on the base member to limit horizontal rotation to less than 360 degrees. However, there is a “dead spot” in the aiming pattern of the light fixture that occurs because of the thickness of at least one of the stop members. It is further desirable to provide horizontal adjustment through at least 360 degrees.